Plastic films and coatings are used for a wide variety of purposes. Examples of potential uses for plastic films and coatings include food packaging, as liners for the packaging of industrial products, shopping and garbage bags, agricultural films, construction films, photographic films, x-ray films and magnetic audio and video recording films.
Plasticulture, defined as the use of plastic materials for agricultural applications, is a well-known technology in agriculture that has a very long history. There are many examples of plasticulture applications, such as silage bags/wraps, greenhouse films and plastic mulches. Plastic mulch has been widely adopted by farmers around the world as a tool for improving crop yield and quality. In 2013, the Grandview Research consultancy projected that the mulch film segment accounted for 44.3% of the market volume from the $5.9 billion agricultural film market, which is expected to continue growing through 2020 at 7.8% per year.
Silage (bale) wrap films are a common application for film materials in an agricultural context. Silage films are typically ductile and adhesive films that are used to tightly wrap bales of fresh or wilting grass. Forage is typically baled with a fixed-chambered baler into uniformly sized bales, which may be either wrapped with silage film using a bale wrapping machine or inserted into a silage bag. The practice of ensiling forage with plastic is particularly common in the dairy industry, which make use of this practice as a cost-effective option for storing high quality feed for cattle. Silage wrap functions to preserve forage materials in the period between when forage is cut and when it is being used as animal fodder. In practice, the plastic materials used to wrap silage preferably have excellent moisture and oxygen barrier properties. Sealing silage with a plastic film creates an anaerobic environment, which encourages anaerobic acid fermentation conditions that result in the decomposition of complex carbohydrates in forage into simpler sugars that are more digestible by animals.
Another common example for the use of plastic films in agriculture is plastic mulching. Agricultural plastic mulch film is typically a sheet of plastic the width of a planting row, plus an additional width on each side of the row onto which soil is piled to hold the sheet in place. In use, the sheet is rolled out for the entire length of the plant row after which holes are punched into it along the length at intervals suitable for the expected crop. Plastic mulch films are widely used around the world because they protect soil from weeds and pests, help to regulate moisture retention by reducing evaporative losses from soil and reduce fertilizer leaching. Plastic mulch films are particularly effective as weed management tools, limiting weed growth by forming a physical barrier above the soil and by blocking sunlight from reaching growing weeds. Plastic mulch is also an important tool for limiting losses due to drought, helping crops to survive drought stress by limiting evaporative water loss from soils and by blocking the growth of weeds that otherwise would draw moisture away from the target crop. Yield losses due to drought stress are increasing due to climate change and intensive agricultural practices that are leading to soil degradation, which is a driver for the increased use of plastic mulches.
Mulch films, silage wraps and silage bags are usually made from either linear low density or high density polyethylene or polypropylene. These types of plastics are extremely strong and flexible, having very long chain polymerized molecules. Under the effect of the energy supplied by UV light or elevated temperatures, these long chains can be degraded over time. Silage films and bags are typically available in a range of colors, with black, blue and green films particularly common. The incorporation of a black colorant, typically carbon black, in silage films and silage bags limits UV degradation. Increased radial heating of black plastic is potentially desirable in northern climates, as it potentially improves silage fermentation conditions and also helps prevent freezing of silage, which facilitates feeding out during the winter. Mulch films are available in a wider range of colors, with black, white, silver, red, blue, brown, green and yellow films commonly available. The opacity of the film governs the amount of radiation available to heat the soil and the growth of weeds under the film. Different colors produce specific soil and ambient temperature conditions under the film and have specific beneficial and detrimental effects on the growth of a particular crop.
Plastic mulches are typically produced from non-biodegradable olefins such as polyethylene or polypropylene, and are generally considered acceptable for organic agriculture under organic standards as long as they are not incorporated into the soil or disposed of in an environmentally-unfriendly manner. However, a significant drawback to typical synthetic plastic mulches is that they have to be removed after they are used, which is a laborious process, while disposal costs are a significant expense for growers.
Oxo-biodegradable mulch films do not meet international standards for biodegradability and compostability and are not true bioplastics. Oxo-biodegradable films are also unacceptable under any standards for organic agriculture. As they are not biosourced and do not meet standards for biodegradability and compostability, they are not accepted as biosourced biodegradable plastic mulches. Conversely, although they can be considered synthetic plastic mulches, organic standards require that synthetic mulches are removed after the growing season and disposed of in an environmentally benign manner. Microplastic fragments are known to persist in the environment at high levels and can be ingested and incorporated into the bodies and tissues of many organisms, where they can cause harm. Oxo-biodegradable films perpetuate, rather than solve, a significant environmental problem.
Various methods have been devised to produce an agricultural mulch film material that degrades in the soil. U.S. Pat. No. 3,454,510 to Newland et al. (incorporated herein by reference in its entirety) describes a degradable mulch film that is produced by blending a pro-oxidant into a water-soluble polyolefin film, resulting in what is generally referred to as an oxo-biodegradable plastic. Among the pro-oxidants that are disclosed are certain metal acetyl acetonates, metal alkyl benzoylacetates, metal acetyl acetonates, metal stearates and metal oleates. Refinements of this process have been developed, such as a film composition described by Cole et al. (U.S. Pat. No. 3,707,056, incorporated herein by reference in its entirety) wherein petroleum coke is incorporated into the mulch film and released as the film degrades to improve the cation exchange capacity of the soil, furnish nutrients and improve soil quality. The pro-oxidant additives added to oxo-biodegradable plastics cause the plastics to fragment after sunlight or heat exposure. While fragmentation makes plastics more readily biodegradable by microorganisms, the biodegradation process still takes months to decades. These films do not meet international standards for compostability such as ASTM D6400, which requires that 60% conversion of the plastic's carbon is reduced to carbon dioxide within 6 months.
Starch has been used as a base material for producing biodegradable mulch films because starch is inexpensive and abundant and can form a film structure. While starch is a natural polymer, a problem with biodegradable film products that are based on starch blends is their typical inclusion of synthetic petroleum-derived polymers, such as polycaprolactone, within the polymer matrix, which prohibits their use in certified organic production unless the film material is manually removed from the soil at the end of the growing season. Starch-based films typically must be coated or blended with water-resistant polymers because starch films otherwise lose strength if they become saturated with water. For example, U.S. Pat. No. 3,949,145 to Otey (incorporated herein by reference in entirety), describes a mulch film formulation including starch and a synthetic polyvinyl alcohol that is coated with a water-resistant coating composed of polyol-toluene-diisocyanate prepolymer and 1 part of poly(vinylidene chloride-acrylonitrile) copolymer or 1 part of poly(vinyl chloride) resin containing a plasticizing amount of a suitable plasticizer.
U.S. Pat. No. 5,292,782 to Bastioli (incorporated herein by reference in entirety), describes a thermoplastic copolymer of starch and a synthetic thermoplastic polymer, such as polycaprolactone, which can be used to produce a biodegradable mulch film.
Polyhydroxyalkanoates are biologically degradable polymers which can be accumulated by microorganisms as sources of carbon and energy. Poly(3-hydroxybutyrate) (PHB) and the copolymer poly(3-hydroxybutyrate)-co-valerate (PHB/HV) are the most known and best studied forms of polyhydroxyalkanoates and are classified as short-chain-length polyhydroxyalkanoates. However, polyhydroxyalkanoates represent a large class of polymers with over 300 variants.
Various methods have been described for producing films and coatings based on polyhydroxyalkanoates. For example, Waddington (U.S. Pat. No. 5,578,382) and Eggink and Northolt (U.S. Pat. No. 5,958,480), each incorporated herein by reference in entirety, describe methods for producing a biodegradable film from polyhydroxyalkanoates, while Bond and Noda (U.S. Pat. No. 7,077,994, incorporated herein by reference in entirety) disclose a method for producing a film from a blend of polyhydroxyalkanoates and starch. U.S. Pat. No. 6,828,357, incorporated herein by reference in entirety, describes a method for creating porous polyhydroxyalkanoates that have a wider range of biodegradation rates, which makes them more suitable in particular for producing a mulch film.
Various methods have been devised to integrate other compounds into plastic films and coatings that are released through a slow or controlled manner. Byron (U.S. Pat. No. 2,169,055, incorporated herein by reference in entirety) describes a mixture of essential oils in cellulose acetate that could be used to form a fragrance emitting film, while Seiner (U.S. Pat. No. 3,655,129, incorporated herein by reference in entirety) describes the entrapment of minute droplets of volatilizable fragrance oil within a polymeric matrix. Funk and Wang (U.S. Pat. No. 8,759,279, incorporated herein by reference in entirety) describe a method for injecting a fragrance into an extruder and blending it with a starch film. Dobo et al. (U.S. Pat. No. 4,267,138, incorporated herein by reference in entirety) describe a coating that slowly releases biologically active compositions such as pharmaceuticals, while Guo and Martin (U.S. Pat. No. 8,680,228, incorporated herein by reference in entirety) disclose a method for producing polyhydroxyalkanoate polymers capable of controlled release of bioactive agents.
A method for producing a degradable agricultural film that releases plant nutrients in a controlled manner was described by Lahalih et al. (U.S. Pat. No. 4,845,888, incorporated herein by reference in entirety). This method for produces a multi-layer film that releases nutrients to the soil. The first layer of the film is formed from a water-soluble synthetic resin such as polyvinyl alcohol, a releasable form of nitrogen and a releasable form of a plant nutrient in addition to nitrogen. A second layer includes a water-soluble synthetic resin having an average molecular weight which is greater than the average molecular weight of the water-soluble synthetic resin in the first layer, such as polyvinyl acetate, and a releasable form of nitrogen admixed therein. The second layer also includes a thin film of water-resistant polymer to retard the degradation rate of the second layer and to slow the release of nitrogen in the second layer. Dujardin et al. (PCT Publication No. WO/2013/143968 and U.S. Pat. No. 8,372,418) describe a multi-layer polyethylene film that releases a pesticide into the soil through diffusion when used as a mulch film. The agricultural films produced as taught by this method are not biodegradable or compostable.
U.S. Patent Publication No. 20120077254, incorporated herein by reference in entirety), describes the use of spent polyhydroxyalkanoate films or shredded polyhydroxyalkanoate films as substrates for anaerobic digestion. The biogas formed through the anaerobic digestion process may be used for electricity generation, as a fuel for heating, cooking or other purposes, or as a feedstock for polyhydroxyalkanoate production by methane-consuming 01 microorganisms, as described in (U.S. Patent Publication No. 20130071890, incorporated herein by reference in entirety).
Legal et al. (U.S. Pat. No. 3,316,676, incorporated herein by reference in entirety) describe an example of a seed coating method in which vermiculite is mixed with a binder such as polyvinyl acetate. After embedding a seed into this mixture, it is compressed to form a pellet. Alternative approaches have been described by Graves (U.S. Pat. No. 3,707,807, incorporated herein by reference in entirety), who describes a seed coating composition that comprises an aqueous emulsion of a water-soluble neutralized copolymer of an α,β-unsaturated monocarboxylic acid and a lower alkyl acrylate and a crosslinked copolymer of vinyl acetate and a lower alkyl acrylate, while Barke and Luebke (U.S. Pat. No. 4,272,417, incorporated herein by reference in entirety) discloses a seed coating composition comprising a vinyl or alkyl binding agent that is blended into a liquid medium comprising water and a polyol. Danelly (U.S. Pat. No. 4,249,343, incorporated herein by reference in entirety) discloses a water insoluble polymeric microgel that provides protection for the seeds from mechanical and environmental damages and that may be used as a carrier for materials such as fertilizers, herbicides and pesticides.
Useful monomers for the production of microgels that are disclosed by Danelly include acrylic acid; methacrylic acid; hydroxy esters, amino substituted esters and amides of acrylic acid, methacrylic acid and maleic acid; vinylpyridine and derivatives of vinyl pyridine such as 2-methyl-5-vinylpyridine. Obert et al., in U.S. Pat. No. 6,557,298, incorporated herein by reference in entirety, disclose a method for treating a seed with a dry mixture of a hydrogel and an active ingredient. Active ingredients useful for this purpose include pesticides, selective herbicides, chemical hybridizing agents, auxins, antibiotics and other drugs, biological attractants, growth regulators, pheromones, dyes and combinations thereof. The hydrogel and method of application resists loss of coating due to abrasion encountered during handling, storage, transportation, distribution and sowing, and also provides long lasting treatment of the seed with that effect and even, if so desired, provides such treatment to the plant that later emerges from the seed.
U.S. Pat. No. 7,989,391, incorporated herein by reference in entirety discloses a seed coating composition consisting of an aqueous carrier, a pigment colorant, an acrylic latex binder and a fungicide, insecticide, rodenticide, nematocide, miticide or bird repellent, wherein the latex binder is a mixture of methyl methacrylate, styrene, 2-ethylhexyl acrylate, methylol methacrylamide, hydroxyethyl acrylate and methacrylic acid.
U.S. Pat. No. 7,774,978, incorporated herein by reference in entirety, discloses a seed coating with a controlled release rate of an agricultural active ingredient, which is achieved by applying to the seed a film that includes an emulsion of a polymer in a liquid in which both the active ingredient and the polymer have low levels of solubility, and then curing the film to form a water insoluble polymer coating on the surface of the seed.
Encapsulation technologies for intact seeds can also be utilized to improve the propagation of other plants that are difficult or impossible to propagate as seeds by producing synthetic seeds. This approach is particularly common for fruit trees, which are particularly difficult to propagate by planting seeds. One of the problems with fruit trees is that they have a prolonged juvenile phase, which means that breeders must wait for a long time before their crops will produce seeds. Many fruit crops, such as apple trees, are also heterozygotes that are produced by grafting distinct parents to form a hybrid. The seeds produced by these plants have unpredictable variants of their parents' characteristics, and in some cases the seeds that are produced are sterile. Propagation by seed also may be hindered, especially for fruit crops, due to the high dessication-sensitivity of their seeds, minute size, reduced endosperm size, low probability that seeds will germinate, and low tolerance of seeds to long-term storage. Accordingly, Kitto and Janick (Kitto and Janick, 1982, Hort. Sci. 17:448, incorporated herein by reference in entirety) describe a method for producing a synthetic seed by coating a carrot somatic embryo in a mixture of a water-soluble resin, polyoxyethylene glycol (Polyox). Redenbaugh also describes a method for encapsulating somatic embryos in an alginate hydrogel (Redenbaugh, 1984, In Vitro Cell Dev. Biol. Plant. 20:256-257, incorporated herein by reference in entirety). Further development of this technology, and its application to a number of different plant species, is outlined by Rai et al. (Rai et al., 2009, Biotechnology Advances, 27:671-679, incorporated herein by reference in entirety). Noda and Satkowski (WO01094678) describe an application of a polyhydroxyalkanoate copolymer as a coating for agricultural items.
Biostimulants, which are generally defined as formulations of bioactive metabolites and microorganisms that are applied to plants and soils to improve crop vigor, yield, quality and stress tolerance, are a major emerging trend in agriculture, and are increasingly being used by farmers to increase crop health and productivity. The high cost of developing new chemical pesticides, rising insect and weed resistance concerns and growing regulatory and consumer pressure that favors limiting chemicals in the environment are factors that are driving increasing interest in biostimulants. The concept that seed coatings can be used as a delivery system for agricultural chemicals such as fungicides, insecticides, rodenticides, nematocides or miticides is well established. Redenbaugh (U.S. Pat. No. 4,779,376, incorporated herein by reference in entirety), for example, discloses a hydrogel formulation that may be used to encapsulate pesticides, herbicides, insecticides, fungicides, fumigants, repellants, rodenticides, fertilizers, nutrients, sugars, carbohydrates, adenosine triphosphate, microorganisms, growth regulators and hormones around a seed. Various materials may be used to form the gel, such as alginate, carrageenan and locust bean gum.
While past technologies may be effective to a certain degree in providing functionalized biopolymer films and coatings, it remains desirable to provide such films and coatings with enhanced biodegradability and functions to address the various requirements of films and coatings in agriculture and other applications.
Plastic filaments, which are generally defined as threads of plastic, are used to manufacture a wide range of products including, but not limited to, stranded ropes, tooth brush bristles, fabric materials and plastic ties. Plastic filaments are also widely used as feedstocks for three dimensional (3D) printers, and the types of plastics most widely used for this application are typically acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA). ABS is a synthetic copolymer made by polymerizing styrene and acrylonitrile in the presence of butadiene. PLA is a synthetic biopolymer that is typically manufactured from renewable resources such as corn starch and sugar cane.
ABS filaments for 3D printing are generally preferred for printing materials intended to have mechanical uses due to its superior strength, flexibility, machinability and temperature resistance. A significant drawback to ABS is that unpleasant and hazardous odors are produced as it is extruded. It has been shown that ultrafine particulate fumes are produced at a level that is ten times higher when ABS filaments are used in 3D printers than for PLA-based filaments (Stephens et al. 2013. Ultrafine particle emissions from desktop 3D printing. Atmospheric Environment. 79:334-339). PLA filaments are generally available in a wider range of colors and translucencies, which makes them attractive for printing materials intended for display purposes or household uses. However, while PLA meets the ASTM D6400 standard for compostability, which requires that 60% conversion of the plastic's carbon is reduced to carbon dioxide within 6 months, it will only biodegrade quickly if composted in an industrial composting facility configured to heat the material above 60° C. with constant feeding of digestive microbes. PLA does not decompose at an effective rate in simple composting systems.
While past technologies may be effective to a certain degree in providing biodegradable polymer filaments, it remains desirable to provide improved biodegradable polymer filaments with enhanced biodegradability to address the various requirements and improve the safety profile of such filaments.